1. Field of the Invention
The present invention relates to an internal combustion engine provided with an oil filter through which lubricant oil discharged from a positive-displacement oil pump flows. More specifically, the present invention relates to an oil filter including a filter base, an oil filter body attached to the filter base, and a cover for covering the oil filter body.
2. Description of the Related Art
During the maintenance work for an oil filter including a filter base attached to an internal combustion engine and an oil filter body attached to the filter base, such as oil filter body changing work, oil leaks in some cases from the filter base. A known oil filter disclosed in, for example, JP-U 62-45315 includes a filter base provided with an oil guard or a wall to prevent the oil that has leaked from the filter base from contaminating components of the internal combustion engine placed around the filter base.
The volume of the pump chamber of a positive-displacement oil pump is varied to suck oil into and to discharge oil from the pump chamber. Therefore, the pressure of the oil in the discharge passage through which the oil discharged from the oil pump flows pulsates. An oil filter placed in the discharge passage is vibrated by the pulsating pressure of the oil and radiates noise or sound.
If a cover covering the oil filter body is enlarged to reduce the radiation of sound and to enhance the oil stopping effect of the cover, the oil filter cannot be satisfactorily cooled by air around the oil filter and by wind that flows against a vehicle provided with the internal combustion engine when the vehicle runs.
Referring to FIG. 12, when a cylindrical cover b covering an oil filter a formed integrally with a filter base is provided with an opening c extending from an open end part b2 toward a base end part b1 to allow air to flow through the cover b, corners of the edges e of the opening c are likely to be vibrated by the pulsating pressure of the oil in an oil passage formed in the filter base and the sound radiated by the oil filter a. Thus, in some cases, the cover b radiates sound.
When a component member or an engine body of an internal combustion engine is disposed near the cover b opposite to the cover b with respect to a diametrical direction, it is possible that large sound are generated by the resonance of the cover b or the component member or the engine body due to the propagation of the sound generated by the cover b and the sound radiated by the component member or the engine body in a space between the cover b and the component member or the engine body.